Document using VS Code with JCasC JSON Schema

We need documentation explaining how to use JSON Schema in Visual Studio Code. Use-cases to address:

* How to get automatic syntax validation working in your IDE
* How to get autocompletion working in your IDE
* How to get Documentation popups working in your IDE

Acceptance criteria:

- [ ] A documentation page is created (it might be a separate page or a section). It isw referenced from the JSON Schema documentation
- [ ] There is a public demo for JCasC Schema within the repository (sample schema generated by JCasC + sample IDE settings)
- [ ] There is a case study blogpost on jenkins.io about this to improve visibility
- [ ] The feature is announced at the subproject meeting
- [ ] JCasC Dev Tools project page is updated